The invention relates to a method for engaging a gear in a gear position in an automated shift transmission comprising several gears.
Recently, automated shift transmissions have been used in motor vehicles in series. In such automated shift transmissions, the individual gears can be engaged by hydraulic or electric actuators. A gear is typically engaged by having at least one of the actuators move a shifting fork that is mechanically coupled to a shifting sleeve. When engaging a gear, starting from a neutral position N by shifting a shifting fork and therefore the shifting sleeve, a positive interlocking between the shifting sleeve and a shaft to which is it fixed in a relatively non-rotatable manner and a loose wheel of a gear is accomplished. In this positive interlocking state, an internal toothing of the shifting sleeve is engaged by the toothing of a coupling wheel that relates to the gear loose wheel. When this positive interlocking is established and the shifting sleeve has reached its end stop, the shifting fork and the shifting sleeve are in a gear position that is in the following denoted GP.
When passing from the neutral position N into the gear position GP, the shifting fork passes a position that characterizes the start of the so-called pull-in effect (position BE). This pull-in effect is accomplished by a particular shape of the teeth of the internal toothing of the shifting sleeve and/or the teeth of the coupling wheel of the gear's loose wheel. If a torque acts between the shaft and the gear's loose wheel, the shifting sleeve is forced by the shape of the teeth in direction of the gear position GP, or if a gear is engaged already, is held in that gear position GP (pull-in effect). This avoids that the gear might be disengaged in an undesired manner.
For controlling the actuator that can shift the shifting fork typically a sensor for determining the position of the shifting fork is required. For determining the gear position GP of the gears of an individual shift transmission apart from tolerances in the sensor also mechanical tolerances, deviations and play apply, such as for instance axial bearing play as well as shaft and shifting fork deformations. In addition, in the large series production, also variations between the various transmissions in the end stop position occur due to tolerances in the component parts.
Prior art methods for controlling an actuator control the position of a shifting fork to a defined gear position. Due to the existing variances this might result in problems. If for instance during gear shifting action the actual gear position is reached before the apparent gear position on which the control is based is reached, the desired end position appears not to have been reached. This might cause an incorrect error signal. In contrast, the apparent gear position that the control tries to establish might be reached prior to reaching the actually desired gear position. In this case, the danger is that the control turns off too soon while the shifting sleeve has not yet reached the position where the pull-in effect starts, so that the gear can be disengaged in a undesired manner.